Yeah, you should forget about that whole 'superior race' thing, Air. It's just not good to keep the different kinds of humans strictly seperated, I'd compare it with incest in a larger scale. Combining similar genes often leads to predispositions to have the same weaknesses. (Besides, thinking one race is superior is pretty stupid anyway.) See dogs for example: many of todays breeds (created by humans) wouldn't even survive in the free nature. Some even all develop very similar diseases like dachshunds for example (intervertebral disk disease) at a given age. Crossbreeds are often physically tougher and more resistand against illnesses. And finally, trees who grow in a monoculture might all die because of a single reason such as bark beetles, storms or landslides. Mixed woodland on the other side is much more stable and resistand against those things.